This invention relates to molding of synthetic resin to produce features that are integral with a base, and has particular application to the production of fastener elements for touch fasteners and the like.
Hook elements for hook-and-loop touch fasteners and other products are effectively produced by the machine and method of Fischer U.S. Pat. No. 4,794,028. In commercial production, a mold roll is formed by a large number of thin, disk-shaped mold rings (sometimes called mold plates) and spacer rings which are stacked concentrically about a central barrel.
Discrete products are also injection molded with fastener elements extending from a base surface by employing, as part of the mold, a series of stacked mold plates defining an array of mold cavities.
At the periphery of the mold rings or mold plates are cavities for molding the hook elements. In current production machines each cavity of a mold ring has been formed, one at a time, by wire electro-discharge machining (EDM). In the wire EDM process, an electrical discharge between a wire and the plate removes material From the plate while the wire is moved along a specified path to cut a profile through the mold plate. The minimum radius arc that can be cut is determined by the radius of the EDM wire.
Molten resin is forced into the mold cavities, tending to raise the temperature of the mold rings. In practice of the Fischer method, a fluid coolant is circulated through cooling passages within the barrel on which the rings are mounted to remove the heat from the rings. In this way an appropriate temperature of the mold cavities is maintained so that the product becomes sufficiently solid that it can be withdrawn on a continuous basis, typically without opening the mold cavities.